Lecture 12 - Human-Microbe Interactions Flashcards by Stephen McCartney

How many microbes does each human body host?

40 trillion

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What does the following terminology mean

-Microbiota, Microbiome, ‘‘Normal Microflora’’

Microbiota = microflora

-all microbial species

Microbiome

-all microbial species+their function

'’Normal’’ Microflora

-microbes in a healthy human body

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Where do normal microflora live and not live?

LIVE

Skin, respiratory tract, digestive tract, urogenital tract
all exposed to environment

DON’T LIVE

Internal organs
Blood, lymph, nervous system
Not exposed to environment

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Why do normal microflora live in areas exposed to the environment? What kinds of habitat conditions factor into their choice of environment?

Diifferent body areas make for different microenvironments

Habitat conditions

Oxygen levels
Acidity, pH
Available Nutrients

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What kinds of effects can normal microflora have?

Benign (most)

no positive/negative effects
occupy human microhabitats

Beneficial (some)

positive effects
metabolism and defense

Pathogenic (few)

negative effects
cause infectious disease

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How are normal microflora established?

Humans are born without exposure to microbes

-uterus is sterile environment so born without microflora

Colonization of microbes

horizontally transmitted from environment
enters body and grows

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What is a pathogen?

live on/in hosts and cause disease

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what is pathogenicity?

ability of pathogen to cause disease

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what are opportunistic pathogens?

cause disease in the absence of normal host resistance

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what are the surface areas of the normal microflora environments?

Skin

-medium surface area

Oral Cavity

-small surface area

Gastrointestinal tract

-very large surface area

Mucosal tissue

-large surface area

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What kinds of microenvironments does the skin have?

Multiple with different chemical and physical conditions resulting in different populations of bacteria

Sebaceous

upper chest
oily areas

Moist Skin

armpits
high moisture

Dry Skin

forearms
low moisture

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What factors affect the skin microflora?

Host Factors

Age: higher variability and more pathogens in young vs adult
Personal hygeine: more microbes

Environmental Factors

-Weather: affect skin temp and moisture

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What disrupts the normal skin microflora?

Acne

-pore blockage by bacteria

Body Odor

-gases released by microbial metabolism

Disease

-resident microbes prevent pathogen colonization

Mosquitoes

-type of skin microbiome correlates with mosquitoes

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What are the characteristics of the oral cavity?

Heterogeneous Habitat

Antimicrobial chemicals present in oral cavity

-saliva has lysozyme

Nutrient sources

-food particles and cell debris near teeth/gums

High diversity of microbes

Primarily anaerobic metabolism

-facultive and obligate anaerobes

Colonize tooth surfaces

-form bacterial layers, biofilms, called dental plaques

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How are dental plaques and tooth decay related?

Dental plaques that form on teeth undergo anaerobic metabolism and produce lactic acid decaying the teeth

High sugar intake results in tooth decay because fermentation of sugars produce the lactic acid

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How do you prevent dental caries?

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restrict sucrose

-sucrose allows bacteria to produce substance to adhere to teeth

brush teeth

enhance enamel w/ flouride

What are the characteristics of the gastrointestinal tract?

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Heterogeneous Habitat

stomach
small/large intestines

Antimicrobial conditions

-low pH

Lots of Nutrients Sources

-variety of food intake

What is the relationship between pH and oxygen level in the gastrointestinal tract?

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Inversely correlated

low pH = High oxygen level
high pH = low oxygen level

What are the characteristics of the stomach, small intestine and large instestine?

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Stomach

highly acidic, pH=2
only acidophiles survive

Small intestine

fairly acidic, pH=4.5
similar to stomach but more microbes as pH increases

Large intestine

neutral pH = 7
strictly anoxic, no oxygen
largest number of microbes
fermentation vessel

What are the functions of gastrointestinal microbes?

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Vitamin Synthesis

Steroid metabolism

Produce gas

What is microflora turnover?

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10 trillion bacteria removed each day

-fecal matter is 1/3

Remaining populations double 1-2x per day

How is a large intestine similar to a chemostat?

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Open system

Log phase growth

What does disrupting the normal intestinal microflora result in?

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Diarrhea

-side effect of oral antibiotics

Alteration of digestive function

-impaired vitamin synthesis

Pathogen colonization

-no competition from normal microbes

How do we restore normal intestinal microflora?

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Probiotics

Fecal Microbiota Transplant

What are the characteristics of mucosal tissues?

**Heterogeneous habitat** - upper vs lower respiratory - urogenital tract **Antimicrobial conditions** -entrapment, removal, low pH in vagina **Low Diversity of Microbes**

Is the upper or lower respiratory tracts exposed to airborne microbes?

Upper yes but lower no b/c removal by ciliated epithelia cells

Is the urogenital tract exposed to environmental microbes?

**Urethra** -facultative anaerobes **Vagina** **-**lactic acid bacteria that maintain low pH environment

What is virulence and what is pathogenesis?

**Virulence** -measure of pathogenicity **Pathogenesis** -process by which microbes cause disease

How do we measure virulence?

**LD₅₀** - amount of pathogen that kills 50% of hosts - low LD₅₀ = high virulence - high LD₅₀ = low virulence

What is attenuation?

Decrease or loss of virulence -used in vaccines In nature attenuation is selected for -pathogenic to mutualism

What are the steps of pathogenesis?

**Adherence** **Invasion** **Infection**

What is the step of pathogenesis, adherence?

- attachment to host cells - very specific - uses slime layers and pili

What is the step of pathogenesis, invasion?

**Invasion** entering host tissues and causing damage -most invasions occur thorugh wounds **Infection** Growth/production of toxins and virulence factors

What are virulence factors and toxins?

**Virulence Factors** -promote colonization and growth **Toxins** **-**inhibit cell function or kills cells

What are the types of toxins?

**EXOTOXINS** -produced inside released from pathogen cells **ENDOTOXINS** - Not released from pathogenic cells - present in LPS of outer membrane - less toxic than exotoxins

What are the types of exotoxins?

**Cytolytic** -damage cytoplasmic membrane of host cell causing lysis **AB** - INHIBIT INTERNAL CELL FUNCTIONS - most

What are the host barriers to infection?

**Physical** -skin **Chemical** - antimicrobials - low pH **Biological** -competition w/ other microflora

What are the risk factors for host infection to pathogens?

Age, diet, stress

Lecture 12 - Human-Microbe Interactions Flashcards

(38 cards)